The apparent color of an item, such as a shirt or a car, can change dramatically depending on the light shining on the item. For example, a dress can look great under the soft lighting at the store then look ghastly under the harsh fluorescent lights at work. Similarly, people shopping on the internet are often leery of buying something that looks good on their computer screen because they cannot be sure how it will look in real life. The present invention provides systems and methods that help provide accurate color for such items, both on the internet and in other situations including, if desired, determining whether the computer screen is tuned to accurately show the color. Even further, the present invention provides systems and methods can that help show the item under different lighting conditions, such as outside in Seattle on a cloudy day or in Cairo on a sunny day, or even under those fluorescent lights at work. These concepts are discussed in more scientific terms in the following paragraphs.
Discussion of the measurement of light uses a variety of terms and measurement units. Unless otherwise indicated in the text, for example by express statement or by the context, terms relating to measurement and characterization of light and color are defined by reference to Color Appearance Models, Mark D. Fairchild, Focal Press, Addison Wesley Longman, 1998 and the Handbook of Optics, CD-ROM Second Edition, sponsored by the Optical Society of America and published by McGraw-Hill, 1996.
The advent of internet commerce or e-business has resulted in a demand for on-line catalogues of products for consumer and business use. The most active and growth-oriented businesses tend to be technology related. Many customers employed at these businesses use the internet to source products required in their business. Businesses producing catalogues and brochures now require not just photographs and drawings of their products, but digital images suitable for on-line catalogues and brochures. This is one factor, as well as other factors such as digital pre-press and press technology in the printing industry, pushing product photography towards digital imaging. However, photographers that are typically experienced with the color characteristics of film-based systems may not be experienced with digital systems. This can often incur extra uncertainty, costs and delays correcting color in digital images. Additionally, while the product vendor often has control over how the image is captured, there can be a number of problems in the image display process that can interfere with product presentation.
Turning to a general discussion of the nature of light, as well as color, color perception and color imaging, light is a form of energy. It has been described as both electromagnetic waves and photons. The color of light is related to the amount of energy carried by the photon or electromagnetic wave. The color of light is most commonly referred to by its wavelength. Wavelength is typically measured in micrometers (10−6 m) or nanometers (10−9 m). The relative distribution of photons of various wavelengths (or energies) of a given source of light is known as the energy spectrum (commonly abbreviated to spectrum) of the light source.
Examples of light sources include the sun, regular incandescent lights, and fluorescent lights. The solar illumination at the Earth's surface typically varies a few percent across a 20 nm step in the visible wavelength range and intensity of an incandescent filament lamp typically varies no more than 10% across a 20 nm increment of wavelength in this range. Conversely, a fluorescent lamp can have a 20 times (2000%) change in intensity across a step of less than 10 nm. Such variations in energy spectra can present difficulties when trying to provide accurate color rendition of an object.
Similar but less dramatic spikes in illumination profile occur with xenon flash lamps used in photography, and other arc lamp sources. When a lamp with irregular spectral emission illuminates an object with irregular spectral reflection, color appearance can change significantly. For example, as noted above, a dress that looked good under halogen lamps at the store can look terrible in the fluorescent lights of an office. The phenomenon of an object that changes in perceived color under different types of nominally “white light” illumination is known as metamerism. A related effect is the commonly observed greenish cast in the color of a photograph caused by the green spike in fluorescent lights when the film color response is balanced for daylight or tungsten lighting.
The light from the light source shines on a given object; the relative amount of light reflected by an object under illumination is called its reflectance spectrum. The reflectance spectrum is one part of the set of intrinsic color characteristics, which can be referred to as the “intrinsic wavelength-dependent response,” of any given object, such as a car on the street or an apple on a table. Typically, the apparent color of an object to a human eye is a result of the reflectance spectrum of the object under a given energy spectrum. Other factors such as fluorescence can also affect the apparent color of the object. The apparent color of a given object under a given illumination can be referred to as the illumination-dependent color of the object. These and other color characteristics can be measured.
The human eye responds differently to different wavelengths. It is more sensitive to some wavelengths than others. The typical human eye can detect wavelengths of light from about 400 nm to about 700 nm. Human color vision is trichromatic; the eye's color detectors, known as cone cells, detect three overlapping ranges of wavelengths, generally in the red, green and blue ranges. The brain determines the relative response of the three kinds of color-photoreceptors of the eye and interprets this as color.
As technology has evolved people have measured light and color using various instruments. Color rendition in photographic or digital imaging is the process of trying to encode enough of the intrinsic color characteristics of an object being illuminated and imaged so that the human eye, when viewing the object in the rendered image, can interpret the color as intended by the image creator. In order to render color appropriately, the image creator preferably has adequate knowledge of the color characteristics of the light source or illumination, the object being imaged, and the device and recording medium so that the image creator can adjust the image as desired.
These and other concepts relating to light and color characteristics are discussed, for example, in the following references. U.S. Pat. Nos. 5,555,085; 5,369,481; 4,867,563; Handbook of Optics, CD-ROM Second Edition, sponsored by the Optical Society of America, McGraw-Hill, 1996; Professional Lighting Handbook, Second Edition” V. Carlson, S. E. Carlson, Focal Press, Butterworth-Heinemann, 1991; Color Appearance Models, Mark D. Fairchild, Focal Press, Addison Wesley Longman, 1998; Electronic Display Measurement, Peter A. Kellar, John Wiley & Sons, Inc., 1997; Measuring Colour, 3rd Edition, R. W. G. Hunt, Fountain press, England, 1998; Color Technology for Electronic Imaging Devices, Henry R. Kang, SPIE Press, Bellingham, Wash. 1997; Understanding Color, Giordano Beretta, Hewlett-Packard Company, Palo Alto, 2000.
The field of digital imaging has expanded greatly in recent years, particularly in response to the growth of the internet. Products that were previously marketed using printed brochures, catalogs, and in magazine advertisements, are now marketed over the internet via web sites and e-mail. In print media, on the internet and other electronic media (and elsewhere), marketers spend a great deal of time ensuring that the photographic images portraying their products are accurately or appealingly reproduced. Color is a particularly important aspect of product marketing. When such images are digitized and/or compressed for transmission over the internet a great deal of this control disappears and color presentation of products becomes undesirably variable. Additionally, although digital imaging is subject to a number of variables that can degrade image presentation and accuracy, digital imaging provides opportunities to control and correct images. There has gone unmet a need to sufficiently define and control how an object's color is presented in a digital image, on the internet and elsewhere.
The present invention can, for example, capture and/or encode accurate intrinsic color characteristics, or intrinsic wavelength-dependent response, of an object. The system associates the color information with an image of the object that can be interpreted by hardware or software such as a plug-in component of an internet browser or other program. The information can be used to condition the image hue for more accurate or desirable color rendition by adjusting color to resemble a variety of possible illumination conditions. Additionally, the software can provide compensation for the characteristics of the image display hardware and hardware settings of the user's system, as well as provide tools to adjust the display system for optimum color rendition. The present invention provides these and other related advantages.